Expandable bone fixation element

Abstract

A threaded bone fastener including a threaded shank, a head extending from the shank, one or more expandable elements, each having a distal end or a proximal end pivotally attached to the shank, the expandable elements being expandable radially outwards from the shank and contractible radially inwards towards the shank, wherein expansion and contraction of the expandable elements does not change an overall length of the shank.

What is claimed is: 
     
         1 . A threaded bone fastener comprising:
 a threaded shank comprising a proximal portion; and   one or more expandable elements, each having a distal end or a proximal end pivotally attached to said shank, said expandable elements being expandable radially outwards from said shank and contractible radially inwards towards said shank, wherein expansion and contraction of said expandable elements does not change an overall length of said shank.   
     
     
         2 . The threaded bone fastener according to  claim 1 , wherein said expandable elements are threaded. 
     
     
         3 . The threaded bone fastener according to  claim 1 , wherein said expandable elements are not threaded. 
     
     
         4 . The threaded bone fastener according to  claim 1 , wherein said expandable elements are spaced 180° apart. 
     
     
         5 . The threaded bone fastener according to  claim 1 , wherein said shank is fully threaded over its length. 
     
     
         6 . The threaded bone fastener according to  claim 1 , wherein said shank is partially threaded over its length. 
     
     
         7 . The threaded bone fastener according to  claim 1 , further comprising an actuator operative to expand said expandable elements radially outwards from said shank. 
     
     
         8 . The threaded bone fastener according to  claim 7 , wherein said actuator comprises a central rod with a cam, wherein distal advancement of said actuator through said shank causes said cam to push against said expandable elements and expand them radially outwards. 
     
     
         9 . The threaded bone fastener according to  claim 7 , wherein said actuator is accessible through said proximal portion. 
     
     
         10 . The threaded bone fastener according to  claim 1 , wherein said expandable elements are lockable. 
     
     
         11 . The threaded bone fastener according to  claim 1 , wherein a distal end of each said expandable element is connected to said shank, and a proximal end of each said expandable element slides axially with respect to said shank upon radially outward expansion of said expandable elements. 
     
     
         12 . The threaded bone fastener according to  claim 1 , wherein a proximal end of each said expandable element is connected to said shank, and a distal end of each said expandable element slides axially with respect to said shank upon radially outward expansion of said expandable elements. 
     
     
         13 . A bone fastener comprising:
 a shank comprising a proximal portion;   one or more expandable elements, each having a distal end or a proximal end pivotally attached to said shank, said expandable elements being expandable radially outwards from said shank and contractible radially inwards towards said shank, wherein expansion and contraction of said expandable elements does not change an overall length of said shank;   an actuator operative to expand said expandable elements radially outwards from said shank, wherein said actuator comprises a central rod with a cam, wherein distal advancement of said actuator through said shank causes said cam to push against said expandable elements and expand them radially outwards, and wherein said actuator is accessible through said proximal portion.   
     
     
         14 . A threaded bone fastener comprising:
 a threaded shank comprising a proximal portion; and   one or more expandable elements attached to a central, elongate actuator, wherein pushing or pulling of said actuator causes said expandable elements to expand outwards or contract inwards, and wherein expansion and contraction of said expandable elements does not change an overall length of said shank, and wherein said actuator comprises a central portion of said fastener.   
     
     
         15 . The threaded bone fastener according to  claim 14 , wherein said one or more expandable elements comprise prongs. 
     
     
         16 . The threaded bone fastener according to  claim 14 , wherein said one or more expandable elements comprise an elastic spiral. 
     
     
         17 . The threaded bone fastener according to  claim 14  wherein said shank is at least partially threaded. 
     
     
         18 . The threaded bone fastener according to  claim 1 , wherein said one or more expandable elements expand outwards in a combination of radially-directed expansion plus another direction that is not radial with respect to a longitudinal axis of said shank.